Currently, most of the commonly known wide-angle lenses with an angle of view over 100 degrees have a structure starting with a negative diopter. For example, the commonly known Japanese Patent Publication No. 2011-102871, starting from an object side, consists of a first lens group having a negative diopter, a second lens group having a positive diopter, and a third lens group having a positive diopter. When an object moves closer from infinity, the second lens group moves towards an image, and the third lens group moves towards the object to realize focusing. However, there are a lot of lenses in the first lens group and the second lens group, and especially, a second focusing quantity is too large, resulting in an excessively heavy weight of lenses and high focusing load, and a focusing speed cannot be ensured. Moreover, because there are too many lenses, the lens is large in size and high in costs, and cannot be regarded as a miniaturized high-performance wide-angle lens.
Further, the commonly known Japanese Patent Publication No. 2013-20073, starting from an object side, consists of a first lens group having a negative diopter, a second lens group having a negative diopter, and a third lens group having a positive diopter. When an object moves closer from infinity, the second lens group move towards an object space to realize focusing. As a spatial requirement for focusing needs to be guaranteed, enough space is needed for the first lens group and the second lens group; the angle of view of an ultra wide-angle lens is very large, which leads to an extremely large aperture of the first lens group, so that a miniaturized ultra wide-angle lens cannot be achieved.